This invention relates to novel compositions of matter containing optically pure (S)-lomefloxacin. These compositions possess potent activity in treating various infections while avoiding adverse effects associated with racemic lomefloxacin including but not limited to headache, stomach discomfort, gastrointestinal disorders, hypoglycemia, renal and hepatic dysfunction, allergic reactions and respiratory distress, and arthropathy, such as cartilage lesions and erosion and abnormalities in bone growth in immature patients. Additionally, these novel compositions of matter containing optically pure (S)-lomefloxacin are useful in treating infection in those patients with impaired renal function. Also disclosed are methods for treating the above-described conditions in a human while avoiding adverse effects that are associated with the racemic mixture of lomefloxacin, by administering the (S)-isomer of lomefloxacin to said human.
Steric Relationship and Drug Action
Many organic compounds exist in optically active forms, i.e., they have the ability to rotate the plane of plane-polarized light. In describing an optically active compound, the prefixes D and L or R and S are used to denote the absolute configuration of the molecule about its chiral center(s). The prefixes d and 1 or (+) and (xe2x88x92) are employed to designate the sign of rotation of plane-polarized light by the compound, with (xe2x88x92) or 1 meaning that the compound is levorotatory. A compound prefixed with (+) or d is dextrorotatory. For a given chemical structure, these compounds, called stereoisomers, are identical except that they are mirror images of one another. A specific stereoisomer may also be referred to as an enantiomer, and a mixture of such isomers is often called an enantiomeric mixture. A 50:50 mixture of enantiomers is referred to as a racemic mixture.
Stereochemical purity is of importance in the field of pharmaceuticals, where 12 of the 20 most prescribed drugs exhibit chirality. A case in point is provided by the L-form of the xcex2-adrenergic blocking agent, propranolol, which is known to be 100 times more potent than the D-enantiomer.
Furthermore, optical purity is important since certain isomers may actually be deleterious rather than simply inert. For example, it has been suggested that the D-enantiomer of thalidomide was a safe and effective sedative when prescribed for the control of morning sickness during pregnancy, and that the corresponding L-enantiomer was a potent teratogen.
Racemic Lomefloxacin
Lomefloxacin is described in U.S. Pat. No. 4,528,287 and Japan Patent Publication No. 64979 (1985). Lomefloxacin is currently available commercially in the United States as MAXAQUIN(copyright) as well as in Argentina, Japan, Mexico and certain countries in Asia and Eastern Europe, as the racemic mixture, i.e., it is a 1:1 mixture of optical isomers. It is the optically pure, or substantially optically pure (S)-isomer of lomefloxacin, which is the subject of the present invention, hereinafter referred to as (S)-lomefloxacin.
Racemic lomefloxacin, having the chemical name 1-ethyl-6,8-difluoro-1,4-dihydro-7-(3-methyl-lpiperazinyl)-4-oxo-3-quinolinecarboxylic acid, belongs to the quinoline class of antibiotics. The quinoline antibiotics, in general, exhibit a broad spectrum of antibacterial action, demonstrating effectiveness against both Gram-positive and Gram-negative bacterial strains. Quinoline antibiotics have been shown to be effective in treating infections of the respiratory, genito-urinary, and gastrointestinal tracts. They have also demonstrated utility in the treatment of patients with cystic fibrosis and pulmonary infections. Effectiveness has also been demonstrated in the treatment of intra-abdominal, bone and joint, skin, soft-tissue, pelvic, and eye, ear, nose, and throat infections.
Examples of Gram-positive bacteria include but are not limited to Streptococcus, Staphlococcus, Mycobacteria, Listeriaceae, Bacillus and Nocardia. A number of Gram-positive bacteria cause respiratory tract infections including, but not limited to, Streptococcus pneumoniae and Mycobacteria. The majority of clinically diagnosed cases of pneumonia are caused by Streptococcus pneumoniae. However, recently there has been an increase in the number of pneumonias caused by Mycobacteria. Three different species of Mycobacteria, Mycobacteria tuberculosis (M. tuberculosis), Mycobacteria bovis (M. bovis), and Mycobacteria africanum (M. africanum) can cause a disease state commonly known as tuberculosis. Tuberculosis is a highly contagious disease which is most commonly transmitted by aerosolized respiratory secretions. While infection usually begins in the lungs, mycobacteria can easily spread to other organs as well, including eyes, intestine, pericardium, peritoneum, bone and joints, urinary tract, and lymphatic system. See The Merck Manual, 16th ed., pp. 131-146, Merck Sharpe and Dohme.
In addition to M. tuberculosis, M. bovis, and M. africanum, other species of Mycobacteria include M. chelonei, M. Marinum, M. avium and M. kansasii. 
The quinoline antibiotics derive their activity through inhibition of the bacterial enzyme, DNA gyrase, which is responsible for catalyzing the bacterial DNA supercoiling necessary to pack DNA filaments into bacterial cells. This inhibition causes irreversible chromosome damage leading to bacterial cell death. The selectivity of quinoline antibiotics for bacterial cells is the result of the supercoiling mechanism in eukariotic cells being mediated by a different set of enzymes not susceptible to quinoline inhibition. Quinoline antibiotics are also thought to interfere with proper bacterial cell membrane function, also contributing to cell death.
The first quinoline antibiotic to be commercialized, nalidixic acid, was discovered following the observation that the structurally similar 6-chloro-1H-ethyl-4-oxoquinolone-3-carboxylic acid, a minor by-product of the commercial production of the antimalarial agent chloroquine, exhibited weak antibacterial action. Since the discovery of nalidixic acid, some 7,000 analogues belonging to approximately 16 different ring systems have been synthesized and tested for antibacterial action. From this data, a comprehensive structure/activity relationship has been elucidated.
Structural activity studies have demonstrated that substitution,at position 1 and a carbonyl substitution at position 4 on the quinoline ring appear to be required for antimicrobial activity. No substitution at position 2 and a carboxyl function at position 3 also appear to be required for activity. The only exception appears to be a thiazolidone ring fused at positions 2 and 3. Depending on modification, the presence of additional fused rings, as well as various ring substitutions can be either beneficial or detrimental to activity. 
Racemic lomefloxacin exhibits a broad spectrum of antibacterial action, demonstrating effectiveness against both Gram-positive and Gram-negative bacterial strains. Lomefloxacin has shown to be more effective against Gram-negative bacteria. In particular, lomefloxacin has shown excellent bacteriocidal activity against strains of Enterobacteriaceae, Haemophilus influenzas, Neisseria gonorrhoeae, Branhamella catarrhalis, L. pneumophilia, and good-to-moderate activity against strains of Acinetobacter, Pseudomonas aeruginosa, Staphylococcus aureus and Staphylococcus epidermidis, but poor activity against Pseudomonas cepacia. There is only a low propensity for bacteria to develop a resistance to lomefloxacin by spontaneous mutation. However, development of resistance is facilitated when bacteria are exposed to sub-inhibitory concentrations of the antibiotic.
Lomefloxacin has an average elimination half-life of approximately 8 hours with peak plasma concentrations occurring at approximately 1 hour after oral dosing in humans. Its long half-life and dose proportionality have lead to introduction of lomefloxacin as the first, once-daily 4-quinoline antibiotic.
Furthermore, unlike ciprofloxacin, lomefloxacin does not interfere with the metabolism of theophylline. Likewise, co-administration of ranitidine with lomefloxacin has no effect on lomefloxacin""s pharmacokinetics. However, coadministration of sucralfate with lomefloxacin, presumably through aluminum complexation, does reduce the absorption of the antibiotic. In patients with reduced renal function, lomefloxacin exhibits reduced renal clearance, with a consequential prolongation of the half-life by up to 24 hours. Antibacterial levels of lomefloxacin are therefore maintained in patients with reduced renal function for up to five days.
Little is known about the pharmacology of the individual isomers of lomefloxacin. The pure enantiomer form of ofloxacin, a related quinoline antibiotic, has been studied (Antimicrob. Agents Chemother., 1988, 32(9), 1336-1340). The (S)-isomer of ofloxacin has been reported to be twice as potent a bactericide as the racemate against a variety of Gram-positive and Gram-negative pathogens.
The racemic mixture of lomefloxacin is presently used primarily as an antibiotic agent for treatment of infection of the upper respiratory and urinary tracts. Viral infections of the respiratory tract are acute illnesses with local and systemic manifestations. Coryza (common cold), pharyngitis, laryngitis (including croup), and tracheobronchitis are common respiratory syndromes. See, for example, Merck Manual 5th Ed., p. 169, Merck, Sharpe and Dohme Research Laboratories (1987). Bacterial infections of the lower urinary tract are very common. The majority of urinary tract infections are caused by Gram-negative bacteria. Organisms gaining access to the urethra may colonize on the periurethral glands and produce acute and chronic infection. This condition is termed urethritis. Infections of the prostate gland give rise to the condition prostatitis. Enteric, Gram-negative organisms are the most common cause of prostate infection. Merck Manual 5th Ed., p. 1610, Merck, Sharpe and Dohme Research Laboratories (1987).
Additionally, racemic lomefloxacin has also been used in treating enteritis, sexually transmitted diseases, obstetric and gynecological infections, surgical infections, skin, soft tissue and joint infections, otorhinolaryngologic infections and ophthalmological infections.
Lomefloxacin has been shown to have activity against Mycobacteria tuberculosis, the most common causative agent of the tuberculosis disease. (Piersimoni et al., 1992, xe2x80x9cIn Vitro Activity of the New Quinolone Lomefloxacin against Mycobacterium tuberculosis,xe2x80x9d Am. Rev. Respir. Dis. 146:1445-1447). Piersimoni et al. compared the inhibitory effect of ofloxacin, ciprofloxacin, and lomefloxacin against 79 strains of M. tuberculosis which were susceptible to conventional drug therapy and 11 strains of M. tuberculosis which were resistant to conventional drug therapy. Their data showed that the MIC50 and MIC90 of lomefloxacin in the 79 susceptible strains were, respectively, 0.96 xcexcg/ml and 1.02 xcexcg/ml with a range of 0.5 to 2.0 xcexcg/ml. The MIC50 and MIC90 of lomefloxacin in the 11 resistant strains were, respectively, 1.0 xcexcg/ml and 1.1 xcexcg/ml. Piersomoni et al. concluded that lomefloxacin, orally administered once daily could achieve adequate serum levels to inhibit M. tuberculosis. 
Although lomefloxacin and quinoline antibiotics have several advantages, they also have disadvantages, namely, adverse effects. The adverse effects of quinoline antibiotics in general include arthropathy, headache, stomach discomfort, gastrointestinal disorders, hypoglycemia, renal and hepatic dysfunction, allergic reactions and respiratory distress, and central nervous system effects including convulsions, increased intracranial pressure, and toxic psychoses. The adverse effects of lomefloxacin, in particular, include but are not limited to headache, stomach discomfort, gastrointestinal disorders, dizziness, phototoxicity, and arthropathy, such as cartilage lesions and erosion and abnormalities in bone growth in immature patients. Thus, it would be particularly desirable to find a compound with the advantages of the racemic mixture of lomefloxacin which would not have the aforementioned disadvantages.
It has now been discovered that the optically pure (S)-isomer of lomefloxacin is effective in treating infection in a human. Further, it has also been discovered that the optically pure (S)-isomer of lomefloxacin is effective in treating infection in a human while avoiding adverse effects associated with the administration of racemic lomefloxacin, including but not limited to headache, stomach discomfort, gastrointestinal disorders, hypoglycemia, renal and hepatic dysfunction, allergic reactions and respiratory distress, and arthropathy, such as cartilage lesions and erosion and abnormalities in bone growth in immature patients. The present invention also includes methods for treating the above-described conditions in a human while avoiding the adverse effects that are associated with the racemic mixture of lomefloxacin, by administering the optically pure (S)-isomer of lomefloxacin to said human.